1. Field of the Invention
The present invention relates to a vehicle power supply device which is mounted on a vehicle with an output section connected to a motor that rotates with a driving wheel, which supplies the motor with driving electric power during power running of the motor, and which recovers regenerative electric power of the motor during regeneration of the motor.
2. Description of the Related Art
Conventionally, for example, as a power source of a fuel cell vehicle, there is known a vehicle power supply device in which a fuel cell 100 is connected to a drive motor 103 via a contactor 101 and an inverter 102 and in which a battery 105 is connected in parallel with the fuel cell 100 via a DC-DC converter 104 as shown in FIG. 11(a) (for example, refer to Japanese Patent Application Laid-Open No. 2006-73506 [pp. 4 to 5, FIG. 1]).
This type of vehicle power supply device turns on the contactor 101 (closed state) to supply power to the inverter 102 from the fuel cell 100 and increases or decreases an output voltage of the battery 105 by using the DC-DC converter 104 to supply the output voltage to the inverter 102, during power running of the motor 103. Thereby, the vehicle power supply device assists the fuel cell 100 by using output power from the battery 105 in the case of insufficient output power of the fuel cell 100.
On the other hand, during regeneration of the motor 103, the vehicle power supply device turns off the contactor 101 to disconnect the electrical connection between the fuel cell 100 and the inverter 102 and directly connects the fuel cell 100 to the DC-DC converter 104 in this state to recover the regenerative electric power of the motor 103 to the battery 105 via the inverter 102 and the DC-DC converter 104.
The configuration of the vehicle power supply device, which is shown in FIG. 11(a), is advantageous in a case where the range of use of the output voltage of the fuel cell 100 is higher than the output voltage of the battery 105 and the output voltage of the battery 105 is decreased by the DC-DC converter 104 before use. In this case, however, it is necessary to increase the number of stacks of the fuel cell 100 to increase the output voltage, which leads to a disadvantage of cost increase in the fuel cell 100.
Moreover, as shown in FIG. 11(b), there is known a vehicle power supply device having a DC-DC converter 106, instead of the contactor 101, with the battery 105 directly connected to the DC-DC converter 106 and the inverter 102 without passing through a DC-DC converter (refer to, for example, Japanese Patent Application Laid-Open No. 2000-12059 [pp. 5 to 6, FIG. 1]).
In the configuration of the vehicle power supply device, which is shown in FIG. 11(b), does not have a voltage control means for the battery 105, and therefore when the battery 105 outputs the voltage, the DC-DC converter 106 always needs to control the output voltage of the fuel cell 100 to match the output voltage of the battery 105. For this reason, the vehicle power supply device has a disadvantage that power loss increases along with voltage conversion in the DC-DC converter 106.
Moreover, according to the configuration shown in FIG. 11(b), the use of the DC-DC converter 106 enables a decrease in the output voltage of the fuel cell 100 and therefore it is possible to downsize the fuel cell 100 by decreasing the number of stacks thereof. Decreasing the number of stacks of the fuel cell 100 as described above, however, causes a disadvantage of low responsibility when rapidly increasing output current of the fuel cell 100.
In order to avoid the above conventional disadvantage, there may be a configuration in which the fuel cell 100 is connected to an inverter 102 via a DC-DC converter 110 and a capacitor 111 is connected between output terminals of the fuel cell 100 as shown in FIG. 12.
According to the configuration of FIG. 12, during power running of the motor 103, the power output from the capacitor 111 compensates for transient low responsibility of the fuel cell 100 and the power output from the battery 105 assists the fuel cell 100 and the capacitor 111 in supplying the insufficient output power thereof, thereby enabling the downsizing of the fuel cell 100.
On the other hand, during regeneration of the motor 103, it is possible to charge the capacitor 111 by increasing or decreasing the output voltage of the inverter 102 by using the DC-DC converter 110. Moreover, it is possible to charge the battery 105 by increasing or decreasing the output of a inverter 102 by using the DC-DC converter 104.
In the configuration of FIG. 12, however, when, during regeneration of the motor 103, the DC-DC converters 104 and 110 perform a step-up or step-down operation to reverse the current direction of the DC-DC converters 104 and 110 to enable the current to be applied from the inverter 102 to the motor 103 from a state where the current is applied from the inverter 102 to the capacitor 111 and the battery 105 so that the motor 103 is switched to power running, hunting may occur in output voltage from the DC-DC converters 104 and 110 to the inverter 102 due to a difference in control response to the switching in the current direction of the DC-DC converters 104 and 110.
Moreover, this condition causes a delay in power supply from the inverter 102 to the motor 103 for the required power of the motor 103, for example, according to an acceleration command, which lowers the acceleration performance of a vehicle and thereby deteriorates the drivability and regenerating efficiency.
Moreover, when, during power running of the motor 103, the DC-DC converters 104 and 110 perform a step-up or step-down operation to reverse the current direction of the DC-DC converters 104 and 110 to enable the current to be applied from the inverter 102 to the capacitor 111 and the battery 105 from a state where the current is applied from the inverter 102 to the motor 103 so that the motor 103 is switched to regeneration, a delay in switching of the current direction in the DC-DC converters 104 and 110 causes insufficient recovery of regenerative electric power.